1. Technical Field
The present invention relates to selecting fixed point instructions to issue on a load-store execution unit. More particularly, the present invention relates to selecting a simple fixed point instruction to issue on a load-store execution unit when a load-store instruction is unavailable to issue.
2. Description of the Related Art
Computer systems include dispatch logic that fetches instructions from memory and places the instructions into an issue queue. In turn, issue logic schedules the issue queue's instructions to an execution unit. Issue logic scheduling consists of two steps, which are a wake-up step and a selection step. The issue logic's wake-up step determines when an instruction is ready to issue, and the issue logic's selection step selects one of the ready-to-issue instructions.
Many computer systems use a different issue queue for each execution unit type, such as using a load-store issue queue for load-store instructions that execute on a load-store execution unit and using a fixed point issue queue for fixed point instructions that execute on a fixed point execution unit. For these computer systems, the dispatch logic pre-destines each instruction to a specific execution unit when the dispatch logic places the instruction into a particular issue queue.